Fix missing new statement, causing a undefined throw and bad error message

lib/less/parser/parser.js

@@ -122,7 +122,7 @@ var Parser = function Parser(context, imports, fileInfo) {
             // output. The callback is called when the input is parsed.
             try {
                 parserInput.start(str, context.chunkInput, function fail(msg, index) {
-                    throw LessError({
+                    throw new LessError({
                         index: index,
                         type: 'Parse',
                         message: msg,